1. Field of the Invention
The present invention relates generally to a method of shaping entirely seamless wheel rims made of, for example, an aluminum alloy, with high precision.
2. Description of Relevant Art
Methods of manufacturing seamless rims made of, for example, an aluminum alloy (which will be referred to hereinafter as an Al alloy) for vehicles such as automobiles and motorcycles are already disclosed in Jpananese Patent Laid-Open Nos. 43868/1974 and 42065/1976.
In such methods of manufacturing seamless Al alloy rims, a ring-shaped material is held between a pair of rolls opposed to each other, and one roll is moved toward the other roll so as to gradually reduce the distance between them. The rolls are rotated at the same time so as to roll and shape the material to be of a predetermined cross-section and to be enlarged in diameter. The enlargement of the diameter at the time of shaping the material is restrained by guide rolls arranged on the periphery of the material to be shaped.
The conventional methods of making seamless rims have the following attendant problems.
As the ring-shaped material is rolled and shaped between the rolls, the plastic deformation of the material is so predominantly large in the enlargement direction of the diameter that the diameter exceeds the predetermined dimension while the cross-sectional shape of the rim is not yet completed. Therefore, it is necessary to adjust the rolling so that the diameter may be made to be the predetermined dimension, simultaneously with the completion of the cross-sectional shape of the rim. However, such adjustment is so difficult, and further, because the other periphery restraining guide rolls provided in addition to the rolling rolls are so provided on the periphery only partially, the precision of the outside diameter dimension and circularity is difficult to obtain. Further, a twist or the like occurs. Therefore, after the rim is shaped, further correction work is required, and such work is so difficult and complicated that the number of steps in addition to the essential shaping step are necessarily increased. Also, such work requires excessive equipment and labor. Thus, the conventional methods are not desirable for mass-production and cost reduction of seamless rims. Also, during the correcting step, the obtained rim is likely to have a partial load or elongation and to be reduced in strength.
It may be considered to increase the number of the guide rolls to solve the problems associated with the conventional means. However, even if they are increased, the fundamental solution of the foregoing problems will not be obtained, the structure of the shaping apparatus will only be further complicated, and any effect will be minimal.
In view of the foregoing problems in the conventional methods of manufacturing seamless wheel rims, the present invention has been provided to effectively and fundamentally solve such problems and to obtain a highly effective method of manufacturing seamless wheel rims.